Physiology · MU Sofia

73. Adrenal medulla: hormones, physiological effects and control of their secretion.

Explains the adrenal medulla as a modified sympathetic ganglion whose chromaffin cells secrete the catecholamines epinephrine (about 80%) and norepinephrine (about 20%). It then covers their fight-or-flight effects, including raised glucose, cardiovascular changes, lipid breakdown, bronchial dilation and reduced gut activity, with receptor subtypes and how sympathetic preganglionic input and acetylcholine control release. A list of recap questions closes the note.

Inside: 7 sections · 4 labelled pictures · 20 flashcards · 3 min

Topic 72 of 104 in the MU Sofia syllabus for Physiology (Medicine, Year 2). The free AceMed note covers it in 7 sections, about 434 words (3 min of reading), with 20 flashcards.

In this note

  1. Adrenal Medulla: Hormones, Physiological Effects, and Control of their Secretion.
  2. Adrenal Medulla
  3. Hormones
  4. Physiological Effects of Adrenal Medulla Hormones
  5. Epinephrine vs. Norepinephrine
  6. Control of Hormone Secretion
  7. Recap Questions

Adrenal Medulla

The adrenal medulla is the inner part of the adrenal gland. It makes up approximately 20% of the gland and is derived from neural ectoderm. It is a highly modified sympathetic ganglion. The cells of the adrenal medulla are called chromaffin cells, which are essentially modified postganglionic sympathetic neurons. The adrenal medulla secretes epinephrine and norepinephrine. These hormones are catecholamines.

Hormones

  • Epinephrine (80% of secretion).
  • Norepinephrine (20% of secretion).

Physiological Effects of Adrenal Medulla Hormones

The effects of epinephrine and norepinephrine are similar to the effects of sympathetic nervous system activation, but the hormonal effects last longer. The effects of epinephrine and norepinephrine take seconds to manifest.

  • "Fight or flight" response: The body responds to fear, extreme stress, and intense exercise with massive activation of the sympathetic nervous system, including the adrenal medulla. This is the "fight or flight" response.
  • Increase plasma glucose levels.
  • Increase cardiovascular function:
  • Increase heart rate.
  • Increase blood pressure via vasoconstriction.
  • Increase vasodilation in heart vessels.
  • Increase lipid breakdown.
  • Increase bronchial dilation.
  • Decrease gastrointestinal activity.
  • Muscle glycogen is converted into glucose for rapid energy.

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